Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EST Sun Mar 06 2022 Valid 12Z Wed Mar 09 2022 - 12Z Sun Mar 13 2022 ...Overview... Broad troughing over the CONUS midweek should be reinforced by a couple of potent shortwaves, the first diving into the Northwest Wednesday and another reaching the north-central U.S. Thursday into Friday. These features should press the trough axis eastward late week into the weekend, along with an Arctic cold front that will spread chilly temperatures across the interior West and central U.S. and into the East by the weekend. Expect snow to the northwest of the low from the central Rockies/Plains to the Midwest on Wednesday and Thursday, with less certain potential for wintry weather over the Ohio Valley and interior Northeast Friday and Saturday. Meanwhile showers and thunderstorms are likely in the Southeast through late week before the cold front clears out the moisture by next Sunday. Flow should become somewhat more zonal across the CONUS early next week as the trough lifts out of the East, with weak systems through the northern tier states. ...Guidance Evaluation/Predictability Assessment... Model guidance continues to show fairly good agreement for the overall pattern especially initially in the medium range period given the large scale of the features--strong East Pacific ridging, troughing across the lower 48, and a subtropical high over the Caribbean to ridging in the Atlantic. However, there are some differences in the shortwave details that become impactful by the latter part of the week especially with the timing of the trough's movement and thus the cold frontal timing. Broadly, the GFS model suite is faster with the trough axis and front pressing eastward compared to the ECMWF suite and the CMC. This is shown by most individual ensemble members as well as the operational runs and ensemble means from the 00/06Z cycle, and remained the case in the 12Z guidance that has come in thus far. Given typical model performance, the WPC forecast attempted to take an approach in between but somewhat favoring the ECMWF suite, which slowed the front and trough axis down from continuity a bit. The 06Z GFS was somewhat slower and thus better clustered with other guidance compared to the 00Z run, so preferred the 06Z run. Differences in the trough/front also lead to variability with the strength and progression of Great Lakes low pressure Friday and its eventual track northeastward--overall slower to strengthen and move. As noted in the previous discussion, CMC runs including yesterday's 12Z and today's 00Z end up closing or almost closing off an upper low in the Midwest by Saturday, which is an outlier compared to other guidance that keeps the trough phased with a northern Canada upper low. Thus the CMC was not preferred, but its new 12Z run seems comparatively more in line with consensus. Then there is fairly good model consensus for the ridging initially over the East Pacific to track inland late week, but then get suppressed by shortwave energy approaching or entering the Pacific Northwest by next Sunday, but there are still uncertainties with the timing of shortwaves and surface features there. In summary the WPC forecast began with a multi-model deterministic blend, and gradually transitioned to a blend favoring the ECMWF in terms of deterministic guidance with some 06Z GFS input, and adding and increasing the proportion of the ensemble means, particularly the ECENS mean, to reduce individual model differences. ...Weather Highlights/Threats... A stationary boundary settling across the Southeast and ample moisture and instability from the Gulf of Mexico should keep showers and storms in the forecast Wednesday to early Saturday. Localized heavy rainfall rates are likely in this environment, and flooding/flash flooding may be a threat with heavy downpours, especially where multiple rounds of convection track over the same areas during the period, despite the antecedent dry conditions. Meanwhile, a shortwave moving through the West on Wednesday will continue a threat for heavy mountain snows for parts of the interior West and central Rockies. A low pressure system spinning up in the lee of the Rockies and lifting into the Upper Midwest Thursday-Friday brings a winter storm threat from the central Plains to the Upper Midwest. The elongated upper trough should tap Gulf of Mexico moisture with widespread rain into the East ahead of the cold front on Friday, with some potential for wintry weather on the northern/western side of the precipitation shield, but with low confidence for amounts and placement at this point. The next system coming into the Northwest next weekend is likely to increase rain and mountain snow chances across the Pacific Northwest and northern Rockies. Arctic sourced air will spill into the Plains, with daytime highs 20-30+ degrees below normal as far south as Texas through Friday. Overnight lows across the northern Plains and in higher elevations of the Rockies are likely to be near or below zero for many locations. Ahead of the cold front, above normal temperatures should spread across the eastern third of the country Thursday and Friday before being replaced by below normal temperatures by Saturday following the passage of the cold front. By next Sunday, most of the country should modify closer to normal as upper flow become less amplified, though with lingering cool temperatures in the East and along the Gulf Coast. Tate Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml